Diethylhydroxylamine (DEHA) is probably the most potent stable free radical scavenger known. Recently it has been shown to increase longevity in male and female mice and to inhibit spontaneous malignant tumor formation in female mice and rats when administered by inhalation at 10 ppm for 40 hours per week (10 mg/kg-day) for over two years. DEHA is a compound of low toxicity and therefore has potential to be used as an age retardant in humans. We propose to run a controlled test with DEHA to see its effect on longevity. Groups, each of 100 ICR Swiss Strain mice (50 males and 50 females) will receive DEHA at dose levels of 30, 100, and 300 mg/kg-day in their drinking water starting at ages of 1 1/2, 6, 12, or 18 months. The experiment will be run for 4 years, and the effect of DEHA dose and starting age on longevity will be assessed.